The weather service's prediction of rainy weather for the next few weeks is bad news for fruit tree growers. Besides keeping the pollinating bees in their hives, rainy weather at bloomtime often stimulates certain fungus diseases. One of the most recognizable of those diseases in home orchards is shot hole disease.

Also called coryneum blight, shot hole is an important fungus disease of almonds, apricots, nectarines and peaches throughout the San Joaquin Valley. It may also attack plums and prunes. Shot hole causes spots or lesions on buds, leaves, twigs and fruit, and is most severe when we have warm, wet winters and rainy springs. Spots on young leaves have light green or yellow margins, and their centers often fall out as the leaves grow, leaving the characteristic "shot holes." Leaves may also fall from the tree, especially if they're affected when young. Blemishes on almond or apricot fruit become rough and corky as they get older.

The fungus that causes shot hole survives the dormant season inside infected buds and in twig lesions. The spores produced on lesions are spread around on splashing rain or irrigation water. Under California conditions, twigs and buds of apricots, nectarines and peaches can be infected during rainy weather any time between fall and spring.

Sprinkler irrigation can make shot hole disease worse. If you use sprinklers, make sure their angle is low enough to prevent wetting the leaves and fruit. In almonds, infections of the nuts are a problem only when the tree is being wet by sprinkler irrigation.

Try to remove and destroy infected twigs, buds, blossoms and fruit as soon as you see shot hole symptoms. Look carefully for twigs and buds with symptoms after leaf fall in autumn; infected buds have a varnished appearance. Also, remove fruit and nut mummies (old, shriveled fruit or nuts still hanging in trees) and prune out branches with diseased twigs.

If your trees have not had serious shot hole infections, sanitation may be all you need to do to prevent spring infections. However, if your trees have had serious shot hole problems, it's difficult to find and remove all the infected buds and twigs in the fall. You may want to apply a protectant fungicide such as Bordeaux or fixed copper at about the time of leaf fall, and before the first rains. You can also apply these fungicides to peaches and nectarines at the pink bud stage. However, copper fungicides may injure leaves, so you can only use them for a short time in spring. Synthetic fungicides such as Captan and chlorothalonil are also available for shot hole control, and do not injure leaves.

Peach leaf curl, another fungus disease, also promises to be a problem for peaches and nectarines if rainy weather continues through spring. Protectant fungicides such as lime sulfur or fixed copper will prevent the disease, but must be applied before the buds begin to grow to be effective. If the buds on your peach or nectarine trees are swollen, but have not popped open, you still have time to apply a preventative spray for peach leaf curl.